Face structure of hollow-body metal golf club head

ABSTRACT

The present invention relates to a face structure of a hollow-body, metal golf club head, comprising a face of laterally elongated shape, a crown and a sole plate fixed thereto, and particularly to a face structure having thin-walled areas for extended, stable carry and horizontally stabled trajectory. The face  11  has a thick-walled area  15   a  of uniform thickness formed at the backside thereof, which extends from the heel side to the toe side thereof over the hitting area  16   a , and with thin-walled areas  15   b   , 15   c  of uniform thickness formed above and below the thick-walled area  15   a . An elongated portion  17  for fixing the crown and the sole plate is formed projecting backward on the backside periphery of the face  15.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a face structure of a hollow-body, metal golf club head having a face of a laterally elongated shape with a crown and a sole plate fixed thereto.

[0003] 2. Description of the Related Art

[0004] Traditionally, wood clubs used to traverse great distances have employed a hollow-body, metal club head comprised of a face with a crown and a sole plate welded to its backside. The face has been variously improved to have higher resilience so as to carry a ball much farther.

[0005] For example, a high resilience was realized by means of titanium alloy used as a head material, which has sufficient strength in order for the face to be thin-walled. This is because the thinner-walled face makes the backward elastic deflection δ of the face at impact larger, as shown in FIGS. 2B, 2C with solid line, and therefore it makes the elastic elongation λ (indicated as λv, λh in FIG. 2) of the face, especially near the back surface, larger as a whole, resulting in larger total elastic energy Et (as defined in formula (1) below) accumulated in the face.

Et=αx(k×λ ²)/2+β  (1)

[0006] Here, k is an elastic constant of the face in the direction of the elastic elongation λ, a is a coefficient varying related to the elastic elongation distribution in the thickness direction, and β is an elastic energy due to the other factors.

[0007] On the other hand, in Japanese Patent Laid-open Publication No. Hei 9-192273, as shown in FIG. 3, a face structure improvement realizing higher resilience obtained by decreasing a thickness of an area around a hitting area 23 is proposed. A thin-walled area 25 provided around the hitting area 23 makes not only the hitting area 23 to be of higher strength but also the elastic backward elongation of the face 21 to be larger in all directions.

[0008] However, since the face has generally longer dimension in a horizontal direction than in a vertical direction as shown in FIG. 2, even when it has the thin-walled area 25, the elastic elongation of the face, especially near the face's back surface, is larger vertically than horizontally at impact. Thus, the elastic energy Ev due to the vertical elastic elongation λv is large, and the energy Eh due to the horizontal elongation λh is relatively small. In other words, the total elastic energy Et accumulated in the face 21 at impact is not distributed equally to the vertical elastic energy Ev and the horizontal energy Eh.

[0009] Therefore, the carry varies owing to the variation of the total elastic energy Et resulted from the horizontally or vertically deviated hits from hitting area 23, namely, the sweet spot. In other words, the carry of an off-center hit depends not only on the amount of deviation but on the direction of the deviation. Thus, the face structure of laterally elongated shape has tendency of ill stability in a ball carry.

[0010] Furthermore, the ball struck by an off-center hit generally has spin owing to so-called a gear effect. As shown in FIG. 2, the ball impact too close to the heel 23 a of the face 21 results in slicing trajectory, and the ball impact too close to the toe 23 b results in hooking. This gear effect works less when the thickness of the face 21 is smaller. Then the ball trajectory will be stably straight.

[0011] However the face structure 23 having a thin-walled area 25 around the hitting area 23 as shown in FIG. 3 has undesirable characteristics in ball trajectory stability especially because it has thin-walled areas 25 a, 25 b on both lateral sides of the hitting area 23. The contact too close to the heel 25 a increases a slicing spin, and the contact close to the toe 25 b increases a hooking spin, due to the gear effect. Accordingly, this type of face structure is less stable in the ball trajectory of horizontally off-center contact.

SUMMERY OF THE INVENTION

[0012] In view of the above problems, it is an object of the present invention to provide a golf club head having a face structure of laterally elongated shape with thin-walled areas therein, which realizes good stability of the trajectory both in distance and in horizontal direction, as well as sufficient carry.

[0013] In order to accomplish the above and other objects, a face structure of a hollow-body, metal golf club head according to one aspect of the present invention comprises a face of laterally elongated shape, a crown and a sole plate fixed to the face. The face has a thick-walled area of uniform thickness formed at the backside thereof, which extends from the heel side to the toe side thereof over the hitting area, and with thin-walled areas of uniform thickness formed above and below the thick-walled area.

[0014] The area of the thick-walled area may be from 30 to 40% of the total area of the face's backside.

[0015] The vertical width of the thick-walled area may be set from 15 mm to 20 mm.

[0016] An elongated portion for fixing the crown and the sole plate may be formed projecting backward on the backside periphery of the face.

[0017] The elongated portion may have the depth of 15 mm to 25 mm.

[0018] The angle between the face's backside and the elongated portion may be set from over 90° to 100°.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019]FIG. 1A is an elevation of a face structure of a golf club head according to one embodiment of the present invention, and

[0020]FIG. 1B is a sectional view taken on the line B-B in the arrows direction of FIG. 1A;

[0021] FIGS. 2A-2C are the views showing the backward elastic deflection 6 produced at impact in a conventional face of laterally elongated shape, the elastic elongation λv, λh of the face, especially of the face's backside. FIG. 2A is an elevational view in section, FIG. 2B and FIG. 2C are sectional views taken on B-B and C-C lines respectively in the arrows direction of FIG. 2A; and

[0022]FIG. 3A is a side sectional view of a conventional hollow-body, metal golf club head comprising a face which is shaped laterally elongated provided with a thin-walled area, and FIG. 3B is a sectional view taken on B-B in the arrows direction of FIG. 3A.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] The preferred embodiments of this invention will be described in detail with reference to the accompanying drawings. The basic Japanese Patent Application No. 2000-368466 filed on Dec. 4, 2000, the contents of which is incorporated herein by reference. FIG. 1 shows a face structure of one embodiment of the present invention. FIG. 1A is an elevational view thereof and FIG. 1B is a sectional view taken on the line B-B in the arrows direction of FIG. 1A.

[0024] As shown in the drawings, a club face 11 in this embodiment comprises a neck 13 connected to a shaft, a face 15, and a backward elongated portion 17 projecting from the entire periphery of the face's backside. These are forged integrally from titanium alloy. Then a crown and a sole plate (not shown) are welded to the elongated portion 17 so as to form a hollow-body structured golf club head.

[0025] The face 15 is shaped laterally elongated, namely, has longer width horizontally than vertically. A thick-walled area 15 a of uniform vertical width is provided projecting from the backside of the face 15, which is extending from the heel to the toe side over a hitting area 16 a at the center of the face. The areas above and below the thick-walled area 15 a are thin-walled areas 15 b, 15 c, as shown in the drawings. These two thin areas 15 b, 15 c are of the same thickness and are of substantially the same area.

[0026] The thickness of the thick-walled area 15 a is set at the appropriate value within 2.3-2.7 mm, and the vertical width thereof is set appropriately within 15-20 mm. Thus, the area of the thick-walled area 15 a is within 30-40% of the total face backside area. On the other hand, the thickness of the thin-walled areas 15 b, 15 c is set at the appropriate value within 1.8-2.2 mm. These values, namely, the area and thickness of those areas are determined in order for the elastic energy Ev of the vertical elastic elongation λv of the face 15 and the elastic energy Eh of the horizontal elongation λh to be sufficiently equal when an expected load of hitting is imposed at the hitting area 16 a. The value of the expected load of hitting is selected according to the target user of the club. In other words, for a general club the average value of some amateur golfers may be used, and for a made-to-order club for particular professional golf player, his own average value should be used.

[0027] The face 15 of such appropriate values will accumulate substantially the same amount of elastic energy at horizontally deviated impact, as the elastic energy at vertically deviated impact. Thus the variation of carries will be reduced, which was caused by the directional variation of the deviation of hits.

[0028] The reason that the face structure 15 of this embodiment is able to sufficiently equalize the elastic energies Eh and Ev, due to the horizontal and vertical elongations λh, λv respectively, is as follows.

[0029] Since the face 15 has the thick-walled area extending from the heel to the toe and the thin-walled areas above and below the thick-walled area, the horizontal elastic constant λh of the face 15 is larger than the vertical elastic constant λv. This difference between λh and λv compensates the difference between the elastic energies Ev and Eh, namely, (Ev-Eh) due to the difference between the elastic elongations λv and λh. Thus, the total elastic energy Et accumulated at the hitting is distributed equally to the energy Eh of horizontal elongation λh and to the energy Ev of vertical elongation λv.

[0030] Since the thick-walled area 15 a is of sufficient, horizontally uniform thickness, even a contact at areas 16 b, 16 c, deviated horizontally from the sweet spot, will not tend to lead to the gear effect with any spin of the ball. Thus, the trajectory will stably go straight without increasing slicing or hooking. In other words, the variation of trajectory direction will be well reduced.

[0031] The elongated portion 17 is formed projecting backward from the entire periphery of face backside, and has generally a cylindrical appearance with the projection projecting 20 mm deep. The angle D1 which the uppermost portion of the elongated portion 17 forms with the face backside is 100°. The angle progressively decreases downward and is minimized at the lowest portion with the angle D2 of 91°.

[0032] The crown and the sole plate are welded to the edges 17 a, 17 b of the projecting elongated portion 17. Since the weld zone is located apart from the face 15 by the depth of the projection and defects in welding and/or a heat-affected zone by welding are prevented, the face 15 will be free from degradation in strength and toughness therein.

[0033] Moreover, since the angle D which the backside of the face 15 forms with the elongated portion 17 is set to be obtuse under 100°, the span between the hitting area 16 a and the edge 17 a, 17 b of the face portion 11 will be relatively large taking the dimension of the face 15 into consideration. Thus, faster swing speed of the head and higher resilience of the face are accomplished by means of little aerodynamic drag against the face 15 and large bending moment by the hitting on the face 15, respectively. This results in further improvement in a ball carry.

[0034] The reason why the smallest angle, 91°, is small as compared to the uppermost angle of 100° is that the aerodynamic drag at the lowest portion, which has maximum swing speed, should be as small as possible to retard the deceleration of the head.

[0035] Though this embodiment's face 15, whose thickness is 2.3-2.7 mm even at the thick-walled area, is significantly thinner than the usual casting titanium alloy face, whose thickness is 2.8-3.0 mm, it has still sufficient strength. This is because the embodiment's forged face portion 11 is improved in strength than a conventional cast face by approximately 20%, and because the face 15 has relatively high strength and toughness since the crown and the sole plate are welded to the elongated portion projecting therefrom. Such thin-walled face structure of this invention has realized improved resilience and extended carry.

[0036] According to one aspect of the invention, since thin-walled areas are provided above and below the thick-walled area in the face, the vertical elastic constant kv of the face is smaller than the horizontal elastic constant kh. Therefore, as can be understood with the above-mentioned formula (1), the elastic energy Ev will become smaller, which results in substantially equal distribution of the total energy Et into the vertical energy Ev and the horizontal energy Eh.

[0037] Thus, the variation of the ball distance due to the variation of direction of deviation from the face center will be reduced since the face's total elastic energy of horizontally off-center impact and vertically off-center impact are substantially the same.

[0038] Moreover, since the thick-walled area, extending from the heel to the toe, has uniform and sufficient thickness, the gear effect, due to the horizontally off-center contact, will be reduced. Thus, the ball will scarcely have spin, and therefore the trajectory will be stably straight with little slicing or hooking.

[0039] According to another aspect of the invention, decrease in durability of the face due to insufficient thick-walled area is modified since the thick-walled area has over 30% of the total area, and on the other hand, decrease in the resilience due to the insufficient thin-walled area is also modified since the thick-walled area has less than 40% of the total area.

[0040] According to yet another aspect of the invention, since the vertical width of the thick-walled area is over 15 mm, the face has greater durability due to the sufficient width being resistant to strong impact, and additionally, wider area free from gear effect realizes more stable and straight trajectory. On the other hand, since the same width is up to 20 mm, good resilience is realized by modifying the decrease of resilience due to insufficient area of the thin-walled area.

[0041] According to further aspect of the invention, since the crown and the sole plate are fixed to the elongated portion, the fixing portion is apart from the face. Thus, the defects or weakening of fixing, for example poor welding or thermal degradation caused by welding, are prevented from being occurred in the face, resulting in prevention of decrease in strength and toughness of the face, which requires sufficient impact resistance.

[0042] Furthermore, as the strength and toughness are improved, the thickness of the face is able to be smaller so as to realize better resilience.

[0043] According to another aspect of the invention, since the elongated portion has the depth of over 15 mm, the fixing zone is located sufficiently apart from the face. Thus the face will have sufficient strength and toughness even with poor welding or thermal degradation in the fixing zone. Additionally, since the elongated portion has the depth of under 25 mm, this portion is able to be deep drawn, by presswork or the like, integrally with the face so as to reduce the manufacturing cost significantly.

[0044] According to further aspect of the invention, since the angle which the face's backside forms with the elongated portion is set at obtuse angle under 100°, the span between the hitting area and the edge of the face is large considering the dimension of the face. Thus, faster swing speed of the head and higher resilience of the face are accomplished by means of little air resistance against the face and large bending moment of the face caused by load of hitting, respectively.

[0045] Having described a specific embodiment of the invention, the invention should not be taken limitative by any of the details of the description and various changes and modifications may be made without departing from the spirit and scope of the invention.

[0046] For example, the upper and lower thin-walled areas may be of different thickness, though they were equal in the above embodiment, as long as the elastic energy is equally distributed in horizontal and vertical directions. When the lower thin-walled area is thicker, for example, the center of gravity will descend, resulting in the advantage that the ball will be brought higher easily. 

What is claimed is:
 1. A face structure of a hollow-body, metal golf club head comprising: a face of laterally elongated shape; a crown and a sole plate fixed to said face; said face having a thick-walled area of uniform thickness formed at the backside thereof and thin-walled areas of uniform thickness formed above and below said thick-walled area, the thick-walled area extending from the heel side to the toe side of said face over the hitting area.
 2. A face structure of a hollow-body, metal golf club head as claimed in claim 1, wherein the area of said thick-walled area is from 30 to 40% of the total area of said face's backside.
 3. A face structure of a hollow-body, metal golf club head as claimed in claim 1, wherein a vertical width of said thick-walled area is set from 15 mm to 20 mm.
 4. A face structure of a hollow-body, metal golf club head as claimed in claim 1 or 2, wherein an elongated portion for fixing said crown and said sole plate is formed projecting backward on the backside periphery of said face.
 5. A face structure of a hollow-body, metal golf club head as claimed in claim 3, wherein an elongated portion for fixing said crown and said sole plate is formed projecting backward on the backside periphery of said face.
 6. A face structure of a hollow-body, metal golf club head as claimed in claim 4, wherein said elongated portion has depth of 15 mm to 25 mm.
 7. A face structure of a hollow-body, metal golf club head as claimed in claim 5, wherein said elongated portion has depth of 15 mm to 25 mm.
 8. A face structure of a hollow-body, metal golf club head as claimed in any one of claims 4 to 7, wherein an angle between said face's backside and said elongated portion is set from over 90° to 100°. 